The present invention relates to the molding of tires. In particular, it pertains to methods and apparatus for molding a tire bead using a radially expandable bead molding ring.
Reference is made herein to an xe2x80x9cundercutxe2x80x9d bead, referring to the shape of the bead base (the radially inner surface of a tire bead that seats in the bead seat portion of a wheel rim). Tire bead bases are most commonly substantially flat and are angled from zero to several degrees relative to the axial direction with the bead base angle opening axially outward. An undercut bead base may be similarly shaped except that the bead base angle opens axially inward. Examples of tires with undercut bead bases, and examples of wheel rims using such tires, are seen in U.S. Pat. No. 6,092,575. In particular, it should be noted that a common variant of a tire with the undercut bead base design comprises beads of two different diameters on the same tire.
In order to mold certain tire constructions, such as those having undercut beads, it becomes necessary to introduce a portion of the tire mold known as the bead molding ring or counter-molding ring into the interior of the tire in order to engage a molding surface against the bead base. In the prior art, means are known for accomplishing the molding of an undercut portion of a tire bead. For example, U.S. Pat. No. 5,129,802 proposes using two counter-molding rings (bead molding rings) for the axially and radially inner portion of the bead, said rings being continuous. In order to introduce the counter-molding rings into the interior of the tire, it is necessary to deform the raw blank of the tire by ovalizing at least one of the beads, so that the bead can be made to pass beyond the counter-molding ring or rings.
Rings for molding the radially and axially inner portion of a bead have also been described in connection with so-called membrane-less vulcanizing presses. See, for example, U.S. Pat. No. 4,236,883 (referred to hereinafter as the ""883 patent), which discloses such rings, in this instance made in several segments circumferentially adjacent in molding position. These rings are radially retractable so that they can be introduced into the tire interior without requiring deformation of the tire beads. The ""883 patent describes a mechanism occupying integrally the inner volume of the press, so that the necessary movements can be imparted to the several ring segments in order for said segments to accommodate a closing or opening movement in sequence. By a xe2x80x9cmovement in sequencexe2x80x9d is meant that, from a configuration in which the mold is open, the segments do not all go to their molding position at the same time. A first group is brought to its final molding position, then the segments of a second group are inserted between segments of the first group to make a continuous ring. As seen in the ""883 patent""s FIGS. 1-2, the first and second segments join along axially aligned planar surfaces, and all segments rotate into position by means of bellcranks (66) rotating on pivots (70) in depending clevis"" (74). The bellcranks have cam followers that coact with a multi-faceted linear cam assembly (102) for controlled actuation of the segments mounted on the bellcranks.
U.S. Pat. No. 6,238,193 (referred to hereinafter as the ""193 patent) discloses a mold for a tire and a vulcanizing press fitted to receive said mold: a mold for molding a tire having beads of different diameters, "PHgr"0 being the minimum diameter of the tire area at the bead of smaller diameter, "PHgr"2 being the minimum diameter of the tire area at the bead of greater diameter. The mold has two sidewall plates for molding, respectively, the outer surface of the sidewalls and the outer portion of each bead up to a radially inner limit where the diameter of the tire area is "PHgr"0 and "PHgr"2, respectively, a continuous counter-molding ring to mold the bead of smaller diameter from the said radially inner limit where the diameter of the tire area is "PHgr"0 to an axially inner limit of diameter "PHgr"1, where "PHgr"1 is smaller than "PHgr"2, and a split counter-molding ring to mold the bead of greater diameter from the said radially inner limit where the diameter of the tire area is "PHgr"2 to an axially inner limit of diameter "PHgr"3. As seen in the ""193 patent""s FIG. 1, the tire bead bases are undercut, i.e., "PHgr"1 is greater than "PHgr"0, and "PHgr"3 is greater than "PHgr"2. The split ring includes a plurality of retractable segments adjacent in molding position. A flexible membrane molds the inner surface of the tire in the portion of the inner cavity of the tire between the limit of diameter "PHgr"1 and the limit of diameter "PHgr"3.
As viewed in its FIGS. 2-11, the ""193 patent discloses a complex mechanism for engaging the split counter-molding ring to mold the lower bead (the bead with the greater diameter). The split counter-molding ring is annular and comprises large segments (141) with beveled edges and smaller key segments (142) having corresponding beveled edges. The edges are beveled at an angle to the axial direction (see FIG. 4), so that the key segments can be fitted into the annular ring by moving axially down in between the large segments. After the segments have been fitted together (FIGS. 8-10), the ring is pressed down axially against the lower mold sidewall plate 12 to form the bead area (FIG. 11). A problem with the split counter-molding ring design is a complex set of linkages and mechanisms attached to the mold press that is difficult and expensive to manufacture, and that also makes maintaining and changing the vulcanizing mold in the press a time-consuming and difficult process. As viewed in the ""193 patent""s FIG. 2, the split counter-molding ring (14) comprises first segments (141) each mounted on a rocking arm (52), itself mounted rotatably on the slide (17) that is mounted on the lower frame 22 of the press. A roller (521) mounted on each of the rocking arms acts against a first cam 42 that is integral with the lower membrane plate (32). The second (key) segments (142) are mounted on a guide plate (321) in grooves (53) formed between said guide plate (321) and the first cam (42). A roller (531) is rotatably mounted on each of the second segments and rides against a second cam (43) fixed on the lower frame (22) of the press. The profile of the radially outer surface of said second cam (43) serves to impart a controlled motion for the advance of each of the second segments (142).
It is an object of the present invention to overcome the problems and limitations of the prior art tire molds, particularly molds using radially expandable bead molding rings, such as for molding undercut beads. Problems to be solved include reduction of mechanical complexity to simplify manufacturing of the molds, and to ease mold/press maintenance and changeover.
According to the invention, a method is disclosed for providing a two-stage movement for engagement of an expandable bead molding ring with a sidewall molding plate to form a bead molding pocket in a tire mold within a mold press; wherein a first stage of movement comprises radial expansion of the bead molding ring to form a circumferentially continuous outward-facing bead molding surface that is positioned axially inward of the sidewall molding plate; and a second stage of movement comprises pressing the bead molding ring axially outward to engage the bead molding surface with the sidewall molding plate, thereby forming a bead molding pocket for molding a green tire bead; the method comprising the steps of: using axial movement of the mold press to cause both the first stage and the second stage of movement; resisting the first stage of movement with a first set of springs; providing first stopping surfaces for halting the first stage of movement when the circumferentially continuous outward-facing bead molding surface is formed; resisting the second stage of movement with a second set of springs; providing the second set of springs with spring resistance sufficient to prevent axial movement of the bead molding ring until after the first stage of movement is halted by the first stopping surfaces; and providing second stopping surfaces for halting the second stage of movement when the bead molding pocket has been formed.
According to the invention, the method further comprises the step of providing a cam surface on the bead molding ring for dividing an axial force from the mold press into radial force components and axial force components for causing corresponding radial movements and axial movements of the bead molding ring.
According to the invention, the method further comprises the steps of: using the second set of springs to cause axial disengagement of the bead molding surface from the sidewall molding plate when axial movement of the mold press removes force from the second set of springs; and using the first set of springs to cause radial retraction of the bead molding ring when axial movement of the mold press removes force from the first set of springs.
According to the invention, an expandable bead molding ring assembly is disclosed for a tire mold in a mold press that is configured to mold a green tire comprising a tread, two beads, and two sidewalls extending between the beads and the tread; the expandable bead molding ring assembly characterized by: a first annulus that is a segmented bead molding ring, comprising a plurality of segments that radially expand to form a circumferentially continuous radially outward-facing surface for molding one of the beads, and a radially inner frustraconical cam surface for dividing axially-directed forces into a radial force component and an axial force component; a second annulus, concentric and axially adjacent to the first annulus, that is a top spring plate, comprising radially-oriented radial springs that are attached to all of the plurality of segments for controlling radial movement of the plurality of segments; and a third annulus, concentric and axially adjacent to the second annulus, that is a bottom spring plate, comprising axially-oriented axial springs acting between the second annulus and the third annulus for controlling axial movement of the plurality of segments.
According to the invention, the expandable bead molding ring assembly is further characterized by a fourth annulus having a frustraconical radially outer cam surface that is complementary to the radially inner cam surface of the first annulus, wherein: the fourth annulus is attached to the mold press such that the mold press will impart axially directed movement and axially directed forces to the fourth annulus; and the radially outer cam surface of the fourth annulus is positioned concentrically within the first annulus such that the radially outer cam surface of the fourth annulus bears on the radially inner cam surface of the first annulus for applying the axially directed forces from the mold press to the cam surface of the first annulus.
According to the invention, the expandable bead molding ring assembly is further characterized by: a plurality of tee-shaped guide slots in the first annulus opening toward the adjacent second annulus, wherein a wider crossbar portion of the tee-shape has radially aligned slot guide surfaces; and a plurality of guide tees protruding from the second annulus toward the adjacent first annulus, shaped and dimensioned to fit inside the tee-shaped guide slots, the guide tees comprising a crossbar having tee guide surfaces complementary to the slot guide surfaces for holding the segments of the first annulus at a fixed axial distance from the second annulus while also allowing the segments to slide radially in and out.
According to the invention, the expandable bead molding ring assembly is further characterized by: a plurality of guide bolts that slidingly pass through axially-aligned guide holes in the third annulus and are attached to the second annulus, for holding the second and third annuluses concentric and axially adjacent while guiding movement of the second annulus in an axial-only direction. Preferably there is also a bolt head on each guide bolt; and a cavity that widens each guide hole in the third annulus, such that the bolt head has clearance to move axially within the cavity but limits the axially inward movement of the second annulus that is attached to the guide bolt, when the bolt head stops against the end of the cavity.
According to the invention, the expandable bead molding ring assembly is further characterized by: a plurality of spring hooks attached to the segments of the first annulus such that each spring hook extends to one of the radial springs of the second annulus for interaction whereby the radial springs exert radially-directed force on the segments. Preferably, the radial springs of the second annulus are held in radially-aligned spring holding holes that have hook slots for providing an opening along a side of each spring holding hole such that a spring hook hooks through the hook slot into the spring holding hole to interact with the radial spring; and the radial springs exert a radially-inward directed force on the segments of the first annulus. Further preferably, at least one spring hook is used to limit the extent of radial movement of the segments of the first annulus when the spring hook stops against an end of the hook slot.
According to the invention, the expandable bead molding ring assembly is further characterized in that: each axially-oriented axial spring has one end seated in a first axial spring pocket in the second annulus, and has an other end seated in a second axial spring pocket in the third annulus, such that the axial springs exert a separating force between the second annulus and the third annulus.
According to the invention, the expandable bead molding ring assembly is further characterized in that: half of the plurality of segments of the first annulus are first segments that are complementary to, and circumferentially alternated with second segments; the first segments are wedge shaped, having circumferentially lateral faces that converge towards a radially outward-facing bead molding surface of the bead molding ring, the first segment lateral faces being planar and oriented in an axial direction; and the second segments have lateral faces that are complementary to the first segment lateral faces.
According to the invention, the expandable bead molding ring assembly is further characterized in that: the first annulus, second annulus, and third annulus are concentric to, and radially within an annular sidewall molding plate; a fifth annulus that is an adapter plate is concentric, adjacent, and axially outward of the sidewall molding plate; and the third annulus is attached to the fifth annulus such that a tongue protruding from a radially inner periphery of the fifth annulus is trapped in a groove between flanges and a radially outer periphery of the third annulus.
According to the invention, a mold is disclosed for a green tire comprising a tread, two beads each having a radially inward-facing bead base extending from an axially outer heel to an axially inner toe, and two sidewalls extending between the beads and the tread; the mold comprising: first and second sidewall plates for molding, respectively, an outer surface of each of the sidewalls plus an axially outer portion of each of the beads approximately in to the heel; first and second bead molding rings for molding at least the bead bases of the two beads; and an inflatable vulcanizing membrane for molding the inside surfaces of the tire; wherein the mold is characterized by: at least one segmented bead molding ring that is annular and comprises a plurality of segments that radially expand to form a circumferentially continuous radially outward-facing surface for molding one of the beads in cooperation with one of the sidewall plates and the vulcanizing membrane; and a radially inner frustraconical cam surface for dividing axially-directed forces into a radial force component and an axial force component; an annular top spring plate, concentric and axially adjacent to the segmented bead molding ring, comprising radially-oriented radial springs that are attached to all of the plurality of segments for controlling radial movement of the plurality of segments; an annular bottom spring plate, concentric and axially adjacent to the top spring plate, comprising axially-oriented axial springs acting between the top spring plate and the bottom spring plate for controlling axial movement of the plurality of segments; and an annular lock ring having a frustraconical radially outer cam surface that is complementary to the radially inner cam surface of the first annulus, wherein: the lock ring is attached to the mold press such that the mold press will impart axially directed movement and axially directed forces to the lock ring; and the radially outer cam surface of the lock ring is positioned concentrically radially within the segmented bead molding ring such that the radially outer cam surface of the lock ring bears on the radially inner cam surface of the segmented bead molding ring for applying the axially directed forces from the mold press to the cam surface of the segmented bead molding ring.
According to the invention, the mold is further characterized by: a plurality of tee-shaped guide slots in the segmented bead molding ring opening toward the adjacent top spring plate, wherein a wider crossbar portion of the tee-shape has radially aligned slot guide surfaces; and a plurality of guide tees protruding from the top spring plate toward the adjacent segmented bead molding ring, shaped and dimensioned to fit inside the tee-shaped guide slots, the guide tees comprising a crossbar having tee guide surfaces complementary to the slot guide surfaces for holding the segments of the segmented bead molding ring at a fixed axial distance from the top spring plate while also allowing the segments to slide radially in and out.
According to the invention, the mold is further characterized by: a plurality of guide bolts that slidingly pass through axially-aligned guide holes in the bottom spring plate and are attached to the top spring plate, for holding the top spring plate and the bottom spring plate concentric and axially adjacent while guiding movement of the top spring plate in an axial-only direction.
According to the invention, the mold is further characterized by: a two-stage movement for engagement of the segmented bead molding ring with the tire bead, wherein a first stage of movement comprises radial expansion of the segmented bead molding ring to form the circumferentially continuous outward-facing bead molding surface that is positioned axially inward of the tire bead; and a second stage of movement comprises pressing the segmented bead molding ring axially outward to engage the bead molding surface with the green tire bead and to work with one of the sidewall plates to form a bead molding pocket; first stopping surfaces for halting the first stage of movement when the circumferentially continuous outward-facing bead molding surface is formed; spring resistance in the axial springs sufficient to prevent axial movement of the bead molding ring until after the first stage of movement is halted by the first stopping surfaces; and second stopping surfaces for halting the second stage of movement when the bead molding pocket has been formed.
According to the invention, the mold is further characterized by a mold assembly for switching in and out of the mold press as a single unit comprising: the segmented bead molding ring; the top spring plate, that is concentric and axially adjacent to, and assembled axially outward of, the segmented bead molding ring; the bottom spring plate, that is concentric and axially adjacent to, and assembled axially outward of the top spring plate; an annular adapter plate, that is concentric and radially adjacent to, and assembled radially outward of, the bottom spring plate; and one of the sidewall plates, that is concentric and axially adjacent to, and assembled axially inward of the adapter plate. Preferably, the adapter plate is removably attached to the bottom spring plate by means of a tongue protruding from a radially inner periphery of the adapter plate to be trapped in a groove between flanges and a radially outer periphery of the bottom spring plate; and the adapter plate has an annular registration lip protruding axially toward the adjacent one of the sidewall plates for holding the one of the sidewall plates concentrically aligned to the adapter plate.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.